Generally, variable valve actuation mechanisms open and close an intake or exhaust valve in mechanically operative association with the rotation of a crankshaft of an internal combustion engine and vary the lift characteristic of the intake or exhaust valve in conjunction with the rotation of a control shaft. The variable valve actuation mechanism positions the control shaft with respect to the direction of the cylinder array of the internal combustion engine. Therefore, the mechanism includes an axial direction positioning mechanism configured to maintain the position the control shaft with respect to the cylinder array of the internal combustion engine.
Japanese Patent Application Laid-Open (JP-A No. 2005-226543) discloses a variable valve actuation mechanism. The mechanism includes a stopper mechanism configured to mechanically regulate a rotational range of the control shaft. However, a control target value for electronically controlling the control shaft is set to a range smaller than the mechanical-rotational range provided by the stopper mechanism. The stopper mechanism of JP-A-2005-226543 includes two stoppers and stopper pins configured to abut thereagainst. The two stoppers, respectively, extend along the axial direction of the control shaft, i.e., extending to the side of control shaft, from an actuator plate fixed to the cylinder head, and the stopper pins extend along the radial direction of the control shaft. The two stoppers are spaced apart from each other with a predetermined distance therebetween.
Accordingly the configuration disclosed in JP-A-2005-226543 requires the stopper mechanism and axial direction positioning mechanism to be provided independently from one another. For this reason, a large layout space is necessary, which leads to an increase in the size of the variable valve actuation mechanism.